The present invention relates to a contact adhesive and adhesive system for EPDM and related elastomers. More particularly, the invention relates to an adhesive composition for bonding cured layers of EPDM together, a method for bonding said cured layers of EPDM together and a laminate formed by bonding the layers of EPDM together.
EPDM elastomers have long been of interest for possible use as a roofing material, particularly for the industrial and commercial flat roofing markets. Such elastomers provide significant advantages in flexibility and long term weathering resistance over convention BUR materials composed of tar paper composites which have poor flexibility and only very limited weathering resistance.
However, despite these important advantages, the use of EPDM elastomers in roofing applications has been hampered by certain disadvantages relating to the nature of the elastomer. A major disadvantage of such elastomers is the lack of adhesion of EPDM, especially cured EPDM, to itself. This is a serious problem since in applying EPDM sheets to a roof, it is usually necessary to splice the cured EPDM sheets together. This splice or seam area is subjected to both short term and long term stresses such as those caused by roof movement, heavy winds, freeze-thaw cycling and thermal cycling. Such stresses may manifest themselves in shear forces or peel forces, i.e., the seam peels back with heat producing an open seam under severe conditions or a partially open seam (often referred to as a fish-mouth condition) under less severe conditions.
In view of the foregoing, it is necessary to utilize an adhesive to bond the cured EPDM sheets together. As will be evident from the above discussion, an adhesive for bonding cured EPDM elastomer roofing sheets together must meet a number of requirements which are extremely difficult to satisfy. Thus, the adhesive must provide sufficient peel and adhesive strength to permit the splice formed by bonding the cured EPDM roofing sheets together to resist both the short term and long term disbonding forces or stresses referred to above. Moreover, the adhesive must be resistant to oxidation, hydrolysis and chemical attack from ponded water. Additionally, the adhesive must provide the important property often referred in the adhesive art as "Quick Stick". The term "Quick Stick" as used herein means the characteristics of two sheets of material which have been coated with an adhesive composition to develop virtually immediate adhesive strength when placed in contact with each other.
Quick Stick is an extremely important property in an adhesive which is utilized to splice cured EPDM elastomer roofing sheets together. Thus, adhesive compositions including those of the present invention generally require anywhere from about two (2) to about seven (7) days at room temperature (i.e., 22.degree. C.) to attain maximum adhesive strength. At higher ambient temperature, this time period may be somewhat less but at minimum will generally be at least 24 hours. The conventional procedure for splicing the EPDM roofing sheets together is to make the splice within a relatively short period of time after the adhesive coating has been applied to each sheet, generally within 30 minutes but often less. Accordingly, the adhesive composition must provide sufficient immediate adhesive strength or Quick Stick to permit the splice to withstand stresses from winds, movement, handling by installers, etc. until the adhesive achieves its maximum strength which as indicated will generally take from two (2) to seven (7) days.
Commercial contact adhesives which are conventionally employed for bonding cured EPDM elastomer roofing sheets together generally consist of solutions of neoprene or neoprene-type polymers in aromatic or aromatic-aliphatic solvents containing 2-butanone often along with tackifying resins. However, such adhesives have not proven to be very satisfactory due to their lower than desirable peel adhesion strengths. Thus, the neoprene-type adhesives often provide peel adhesion values of only 1 to 2 lbs. per linear inch.
Pressure sensitive and contact adhesive compositions containing neutralized, partially neutralized or unneutralized sulfonated elastomers, tackifying resins and organic solvents or organic solvent mixtures are known in the prior art as shown by U.S. Pat. Nos. 3,801,531 and 3,867,247.
U.S. Pat. No. 3,801,531 relates to pressure sensitive adhesive compositions which contain thiouronium derivatives of unsaturated elastomers or neutralized, partially neutralized or unneutralized sulfonated elastomers including sulfonated EPDM, tackifying resins including phenol formaldehyde or alkylphenol formaldehyde resins and organic solvents or organic solvent mixtures including a preferred 90:10 mixture of toluene and isopropyl alcohol. However, the patent does not disclose or suggest the use of alkylphenols or ethoxylated alkylphenols in such compositions.
U.S. Pat. No. 3,867,247 relates to adhesive contact cements which contain neutralized, partially neutralized or unneutralized sulfonated butyl elasomers, tackifying resins including phenol formaldehyde or alkylphenol formaldehyde resins and organic solvents or organic solvent mixtures including a preferred 90:10 mixture of toluene and isopropyl alcohol. However, the patent does not disclose or suggest the use of alkylphenols or ethoxylated alkylphenols in such compositions.
The adhesive compositions described in the aforementioned patents while similar in composition to the adhesive compositions of the present invention suffer from a significant disadvantage which materially limits their usefulness as a contact adhesive for bonding cured EPDM elastomer roofing sheets together. As will be seen in the comparative evaluation below, compositions of the type disclosed in the above patents are deficient in Quick Stick properties.
A further disadvantage of the use of EPDM as a roofing material relates to the physical nature of the EPDM roofing material. Almost all of the EPDM sheeting material on the market has been treated with talc, clay or mica to assist processing during manufacture and to prevent sticking of the material in shipping and storage. This surface contaminant must be removed before the adhesive is applied. Accordingly, in addition to the need for an effective adhesive, there is a need for a simple and effective method for removing the contaminant and for bonding the cured surfaces of EPDM together.